Today, there is significant interest in the prediction of the life consumption of individual components in a machine, in particular machines with moving parts, where the term life consumption may be defined as the amount of damage the component may endure without failure. By improving the accuracy of such methods, the applied safety limits may be reduced, and unnecessary replacement of components may be avoided. When applied to an entire fleet (e.g., a military aircraft fleet) the cost savings may be significant as well as allow for an increased operational lifetime. Furthermore, in the unusual event that conventional methods are too optimistic, refined methods may avoid failure of components, thus avoiding uncalculated stops in operation or, even more importantly, accidents.
Examples of interesting applications where improved life consumption predictions may be useful include aircrafts, gas/steam turbines, trucks, loaders, nuclear plants and wind turbines.
A conventional method for predicting the life consumption of a component in a machine is to measure one or a combination of the usage/run time, distance, or count the number of cycles of a predefined load session, or a conservative load session. A load session is the time when the machine is in operation, for example for an aircraft a load session may be defined as flying from point A to point B with a predefined rotor speed variation.
In the field of aircrafts, the life consumption of an engine is sometimes determined by making a “simplified” cycle count, focusing on the usage of a specific engine component. There are also available more specific and at least in some sense more reliable methods where, e.g., ELCF (equivalent low cycle fatigue) cycles for the specific, for example, engine component is determined. Such ELCF cycles may for example be calculated based on the high pressure rotor speed of an aircraft jet engine recorded during a load session. The cycles may be determined by the number of times the high pressure rotor speed exceeds certain selected and predefined rotor speeds. Furthermore, to calculate the ELCF cycles, scale factors are determined for the cycles based on predetermined load sessions. However, a major drawback with ELCF cycles is that the prediction of life consumption will have errors if the actual load sessions experienced by a specific component differs significantly from the predetermined load sessions.
As demands for cost efficiency and reliability increase, the interest in finding better models for predicting life consumption has also increased. This is made specifically apparent as the conventional methods do not take all significant load cycles into consideration. For example, the method of counting ELCF-cycles only considers one engine parameter of the entire engine while the life consumption of the critical components in an engine or machine may vary depending on which loads are most important for the life consumption of respective component.
In order to more accurately determine the life consumption of, e.g., an engine, the life consumption for relevant components in the engine must be determined. In order to determine the life consumption of specific components, more detailed knowledge of conditions in separate parts of the engine is required.
In U.S. Pat. No. 7,197,430, a method is disclosed for determining an engine part life usage of a gas turbine engine life limited part used on an aircraft. The method includes operating a gas turbine engine that includes a plurality of rotating components and a plurality of sensors configured to monitor a plurality of gas turbine engine operating parameters, obtaining outputs from the plurality of sensors, and utilizing at least some of the outputs to calculate the life usage of at least one life limited part to facilitate tracking the life-usage of an individual life limited part on the gas turbine engine that is consumed on a flight by flight basis.
Although providing an improved life consumption calculation in comparison to the prior art method of using ELCF cycles, the solution provided in U.S. Pat. No. 7,197,430, still lacks a way for handling a complete flight mission and all thereto related sensor data, i.e., only snapshots of the flight mission when in different conditions are used for determining an alternative cycle count as compared to determining ELCF cycles.
Accordingly, there is still a need for more thoroughly determination of the life consumption of life limited parts, such as for example a mechanical life limited part in an aircraft.